The yeast cell wall is a crucial structure that proctects the cell against lysis during stress and, as such, is an important target of antifungal drugs. Extracellular structures such as the cell wall are dependent on the secretory pathway to deliver biosynthetic enyzmes and precusors. Pro-protein processing is an important post-translational modification in the secretory pathway and we hypothesize that such processing is required for proper cell wall function. To test this hypothesis, we have initiated a program to study the role of the yapsins, a family of five galactosylphophatidylinositol-linked aspartyl proteases in Saccharomyces cerevisiae, in cell wall integrity. Our preliminary results indicate that the yapsins are, indeed, required for proper cell wall synthesis and maintenance of cell wall integrity. This suggests that the yapsins are a previously unrecognized component of post-translational regulation of cell wall synthesis. Since yapsin homologues have been identified in pathogenic yeast and molds, this suggests that they may represent a new family of antifungal drug targets. To test these hypotheses, we propose three specific aims: (1) Define the role of differential expression and localization in the function of specific yapsins, (2) Identify yapsin substrates involved in cell wall function, and (3) Identify and characterize yapsin homologues in pathogenic yeast. The career development plan described in this proposal is designed to allow the investigator to develop expertise and experience in yeast genetics, techniques in cell and molecular biology, and protease biochemistry. In addition, a didactic program is outlined that is focused on providing additional training in bioinformatics and proteomics as well as preparing the investigator for extending this project into the study of fungal pathogenesis. A team of outstanding collaborators and advisors has been assembled to provide additional mentoring and support as the investigator makes the transition to an independent researcher. [unreadable] [unreadable]